A METHOD AND A DEVICE FOR MEASURING THE NUMBER OF REVOLUTIONS IN TURBO AGGREGATES FOR MOTORS

Abstract: Engine turbochargers operate at extremely hight speeds of the order of 120,000 revolutions per minute, with a highly critical thereshold which must not be exceeded. Measurement of the turbo speeed is of particular importance since turbo bearing life will be shortened drastically if the threshold is exceeded. Since the turbo and engine form a contact unit, access for the use of conventional methods of measurement is extremely difficult. Measurement of the sound generated by the rotating turbocharger has shown that the unit emits a tone which is a function of its speed. Thus, the present invention is concerned with a procedure for measuring the turbocharger speed with the aid of a microphone.

Description: A METHOD AND A DEVICE FOR MEASURING THE NUMBER OF REVOLUTIONS IN TURBO AGGREGATES FOR MOTORS. The present invention relates to a procedure of the type described in Patent claim 1 and a device for implementing that procedure. Engine turbochargers normally operate at extremely high speeds of the order of 120,000 revolutions per minute. To obtain maximum power from the engine, it is essential that the speed of the turbocharger unit be as high as possible; the higher the speed, the greater the quantity of air supplied to the engine. However, the speed is subject to a highly critical threshold which must not be exceeded. If this occurs, bearing life will be drastically reduced by breakup of the lubricating oil film. In predelivery testing of engines, it is desirable to measure the speed of the turbo at full load and to adjust the value by means of a bypass valve to ensure that the threshold is not exceeded. Since the turbocharger is an integral part of both the engine exhaust and intake systems, access for measurement by conventional methods is difficult. In the method used until now, a magnetised nut is mounted on the turbo shaft and the speed of the magnetic field generated as the nut rotates is measured. This method is both time-consuming and unreliable since it is difficult to measure the speed of the field with the desired accuracy; the measuring device or probe, which consists essentially of a pickup, cannot be located sufficiently close to the shaft due to the size of the turbo. The purpose of the present invention is to measure the turbo speed with the aid of a microphone. In tests with a microphone, it has been found that the rotating turbocharger generates a tone whose frequency and amplitude are a function of the speed. The microphone used in the test picks up all sound generated by both the turbo and engine. Low-frequency sound generated by the engine valves, fans, gas flows etc. is removed as far as possible by filtering and the remaining signal contains a turbocharger tone which can be separated by means of a bandpass filter. Since this tone contains too much interference for direct measurement, an electronic tuning fork is instead tuned to the same frequency and that value of frequency is measured. The speed of the turbo may then be determined when the number of turbine blades has been established. This method of sound measurement enables the speed of the unit to be determined quickly and simply without physical intervention in the turbo. The method in accordance with the invention also provides a simple means of checking whether the turbo is running at the correct speed in the course of service work. Under normal circumstances, the speed of the unit falls as the turbine driving the compressor becomes fouled, with an adverse effect on engine efficiency. The speed of the turbo can be measured quickly and simply by the proposed method. The appended drawing shows a block diagram representing a typical embodiment of a device suitable for implementing the procedure defined in patent claims 1 and 2. 1 denotes a microphone intended to be placed in the proximity of the turbocharger whose speed is to be measured. It is not necessary that the microphone be located at the unit; it is sufficient that it be located in the same room or space in which the unit is installed. All of the sound generated by both the turbo and engine is picked up and amplified by means of an amplifier 2 connected to the microphone. A high-pass filter 3 connected to the amplifier 2 is used to filter out all low-frequency sound, such as that generated by the engine valves, fans, gas flows etc., from the signal. A bandpass filter 4 connected to the high-pass filter 3 is tuned by means of a programmable logic unit 5, a digital/analogue converter 6 and a voltage-controlled oscillator 7 to the remaining signal with the highest amplitude. The amplitude is detected by means of an analogue detector 8 connected to the bandpass filter 4. After detecting the amplitude, the detector 8 employs a frequency converter 9 to convert the output signal to pulses which are counted by the programmable logic unit 5. To indicate and count the number of blades on the turbine, one to two displays 13 and a power stage 12, as well as function keys 14, are connected to the programmable logic unit 5. The programmable logic unit 5 can be programmed with an electronic tuning fork if the signal from the bandpass filter 4 contains too much interference or is not of sufficient amplitude. A crystal oscillator 10, which functions as a time and frequency reference, is also connected to the programmable logic unit 5.

Claims: PATENT CLAIMS 1. Procedure for measuring engine turbocharger speed CHARACTERISED IN THAT - the sound generated by turbocharger rotation is picked up by a microphone which is used for speed measurement; - the low-frequency sound generated by engine operation, such as noise from valves, fans, gas flows etc. is filtered out of the microphone signal; - an electronic bandpass filter is tuned to the remaining tone with the highest amplitude; - the frequency of the tone with the highest amplitude is determined, and - with a knowledge of the turbocharger geometry, the value of frequency of the tone with the highest amplitude is converted to turbocharger speed. 2. Procedure as described in patent claim 1 CHARACTERISED IN THAT - an electronic tuning fork is tuned to the tone with the highest amplitude; - the frequency of the tuning fork is determined, and - with a knowledge of the turbocharger geometry, the value of tuning fork frequency is converted to turbocharger speed. Device for implementing the procedure described in patent claim 1 CHARACTERISED BY - a microphone (1) placed in the proximity of the turbocharger and connected to a first amplifier (2), - a high-pass filter (3) for filtering out low-frequency signals, such as sound generated by valves, fans, gas flows etc. as the engine runs, from the microphone signal, - a bandpass filter (4) connected to a high-pass filter (3), which bandpass filter is tuned to the remaining signal with the highest amplitude by means of a programmable logic unit (5), a digital/analogue converter (6) and a voltage- controlled oscillator (7), which amplitude is detected by means of an analogue detector (8) connected to the bandpass filter (4), which detector detects the amplitude and employs a frequency converter (9) to convert the output signal into pulses which are counted by the programmable logic unit (5), - a second amplifier (11) which, following adjustment of the bandpass filter (4) to the signal with the highest amplitude, matches the signal whose frequency is determined in the programmable logic unit (5), and - one to two displays (13) and power stage (12), as well as function keys (14), for indicating and counting the number of blades on the turbine and, as a result, indicating the turbine geometry, for the purpose of determining the turbocharger speed. 4. Device in accordance with Patent claim 3 CHARACTERISED BY - an electronic tuning fork, which is programmed into the programmable logic unit (5) if the signal from the bandpass filter (4) is of insufficient amplitude or varies excessively.

Inventors: ERIKSSON LENNART, ERIKSSON, LENNART
Applicants: ASE AUTOTEST AB, ERIKSSON LENNART, ERIKSSON, LENNART
Application year: 1994
Main classification: G01P3
IPC codes: G01P3